My guess is that both were inspired by the Age of Exploration and the "discovery" of the New World, and that each represents the last work in its respective author's oeuvre.
James, the first part of your sentence is close to the right answer, but I think it's more true of The Tempest than Amerika. Kafka wrote Amerika in the '20s, which is just a little after the Age of Exploration. You are right though that both are the last works of the authors, but that is not what I was thinking of when I posted this.
Both works were written about the New World even though both authors never had a chance to see it. It's a testimony to imagination in general and to the belief in a notion of America as imaginary.
This struck me recently because I have always struggled with divorcing my fiction from nonfiction.
I was going to write a longer answer, but the muse ran away.
Also, a little 411- The Tempest is the only play by Shakespeare that he wrote from scratch. All of his other plays were retellings of known histories, myths and folklore.